My husband inherited his mother's black piano. She was a heavy smoker and religiously used Pledge. I don't think it was ever truly cleaned. Plus, it had fingerprints all over. I tried a couple of things to no avail. I used Murphy's Oil Soap as directed. It didn't work. Finally, I used Murphy's Oil Soap full strength, pouring it directly on the piano where allowed or on the scrubber side of a kitchen sponge. (I protected my carpet with news print paper -- unprinted.) I used a ton of elbow grease. Then I took a damp rag and wiped, rinsed and wiped. You wouldn't believe the years of cigarette smoke and Pledge build-up that came off on that rag. It looks tons better. However, try this method at your own risk. I was desperate and I felt I lucked out.

When we bought our shiny black piano a few years ago, the salesman told us to use the product called Glass Plus. It looks like Windex, but has slightly different ingredients. I have used it for several years on the piano which always looks great and the finish has never been harmed.